Voice inflection detection circuit



June 8, 1965 e. CLAPPER 3,183,383

VOICE INFLEGTION DETECTION cmcuxw Filed Dec. 29, 1961 4 Sheets-Sheet 1FIG. 10

IN VEN TOR GENUNG L. CLAPPER ATTORNEY June 8, 1965 a. L. CLAPPER VOICEINFLECTION DETECTION CIRCUIT 4 Sheets-Sheet 2 Filed Dec. 29, 1961 Elsa52555 EEEE 2 55 LE June 8, 1965 e. CLAPPER 3,188,383

' VOICE INFLEGTIONV DETECTION cmcux'r I Filed Dec. 29, 196i 4Sheets-Sheet 5 June 8, 1965 ca. L. CLAPPER 3,

VOI CE INFLECTION DETECTION CIRCUIT --P2-- cjamslcoml I LH ]BIASICND.IllBlAslf I1 I1 ems I -11 |COND.IBIAS| l L [connlams I IloounII I I E;(I07) 50% (I15) RISING FALLING VOICE CODE OUTPUT 47 OUTPUT I27 159 129 mMEANING HI 1 0 1 1 0 RISING VOICE LLLLL L I L/01 10I I '6Ig FIG. 10 FIG.1b FIG. 10

United States Patent 3,188,338 Vidal-[CE INFLECTIGN DETEQTEGN CIRQUHTGenung L. tClapper, Vestal, N.Y., assignor to International BusinessMachines (Iorporation, New York, N.Y., a corporation of New York FiledDec. 29, 1961, Ear. No. 163,327 7 (Ilaims. (QB. 179-l) The presentinvention relates to an inflection detection apparatus and in particularto an inflection detection apparatus particularly designed to detectinflections in speech.

In relation to speech, the voiced sounds are generated by the vocalchords as air from the lungs is passed through the same. The waveform ofthe sound generated at the vocal chords is a sawtooth which it isrecognized contains all frequencies when analyzed into Fouriercomponents. This sawtooth waveform is not however transmitted as soundexternal to the speaker but is resonated by cavities formed by themouth, tongue, and lips so that the externally generated sound will bethose frequencies contained in the sawtooth which are acousticallyresonant with the sounding box formed by the mouth, tongue, teeth, andlips.

The frequency of the sawtooth is the fundamental pitch. Most men use apitch in the lower part of their vocal ranges, typically from 110 to 140cycles per second. Women and children also use the lower part of theirvocal ranges,.which is an octave higher than men. Therange infundamental pitch in speech is usually small for a given speaker, butinflections occur which may carry more information than the actualpitch.

F or example, consider the following illustrations of inflection as akey to the intelligence contained in a word.

one R-F-S R rising voice seven S-R-F S steady voice eight R-F-R Ffalling voice While the illustrative embodiment is applied particularlyto speech or sound, it should be understood that the invention could aswell be used in detecting inflection in any form of complex wave.

In general the inventive concept of the present invention involves adetecting circuit for the fundamental frequency contained in thewaveform being analyzed and a balanced integrator having an output whichis the. same for no input as for a median frequency input wherein notime is wasted or erroneous indications generated while the modulatorgoes from no input to a median frequency input.

It is therefore an object of the present invention to provide apparatusfor detecting inflection.

It is a further object of the present invention to provide apparatus fordetecting inflection in a complex wave.

Another object of the present invention is to provide apparatus fordetecting inflection in speech.

Still another object of the present invention is to provide apparatusfor detecting the fundamental frequency of the intelligence medium beingmonitored.

Yet another object of the present invention is to provideapparatus formonitoring frequency and providing the same output when the input isZero or at a median frequency.

Another and further object of the present invention is to provideapparatus for monitoring speech, detecting the fundamental frequency ofthe sawtooth waveform contained therein, and generating an outputindicative of inflection wherein the absence of a fundamental frequencyand the presence of a median frequency fundamental pro vide the sameoutput.

The foregoing and other objects, features and advan tages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invenion, as illustrated inthe accompanying drawings.

in the drawings:

FIG. 1, consisting of FIGS. 1a, 1b, and 1c, is a circuit diagram of theinvention.

FIG. 2 is a chart of the waveforms concerned with the balanced modulatorcircuit 94 of FIG. 1b.

FIG. 3 is a chart of the inflection detection logic circuit of FIG. 1c.

FTG. 4 is a chart illustrating how FIGS. la-lc are to be arranged toform FIG. 1.

In general, FlG. 1a discloses a preamplifier responsive to voicefrequencies for providing at 29 a signal of a uniform amplitude. In theprocess of generating a uniform envelope output signal, a feedbackcircuit is provided. An output 47 will have a signal containedthereon'indicative of the variations in magnitude of the input speechfrequencies. Since speech contains a sawtooth amplitude variation at thefundamental frequency of the voice, there will be amplitude variationsin the input signal. Thus signals on line 47 will be at the fundamentalfrequency of the voice. While speech is the input signal used here, itshould be understood that any signal can be monitored, and thefundamental extracted with this inventive concept. Suitablemodifications would of course be made for the range of frequencies beingmonitored.

The fundamental frequency signal on line 417 is shaped by a pulseshaping circuit 86, FIG. 1b, and applied to a balanced integrator 94. Anoutput voltage on output 127 is developed indicating a normal or medianfundamental or a rising or falling fundamental.

This output 127 is applied to a voltage change detector and logiccircuit, FIG. 1c, wherein an output at and/or at 171 is developedindicative of inflection.

This invention forms a part of the invention disclosed in applicationSerial No. 161,089 to Genung L. Clapper. The preamplifier, FIG. 10, isfurther disclosed and claimed in application Serial No. 161,088 toGenung L. Clapper.

In the compression of speech and audio waveforms, there are generallyseveral requirements involved. One of these is that the compressionattack be as fast as possible without to much overshoot, and the otheris that the response after compression be fast to enable: the indicationof the weaker speech sounds. Also a definite level of over-allsensitivity must be established to prevent noise amplification inperiods of silence. This is often not done in regular public addressequipment, the compression usually being rather slow which tendstoaverage out the volume, and it is possible to have considerable delaysboth in the attack and recovery without serious problems. However, inspeech analysis equipment there is needed both a fast attack andrecovery, and furthermore it is desired that no appreciable distortionbe introduced since a frequency analysis is made of the speech waveformand any clipping or other distortion would introduce frequencies whichwould upset any frequency analysis or speech recognition code that mightbe used. Former methods of compression have utilized a gain controloperating upon the first or second stages of a preamplifier. Althoughthis method is eificient, the operation is usually somewhat slow becauseof unavoidable delays produced by the relatively long time constants ofthe coupling networks.

Referring to FIG. 1a, a dynamic microphone It) is shown feeding throughinput capacitors 15 to a preamplifier circuit which comprises twotransistors 17 and 19. These stages are conventional capacitor-coupledgrounded emitter stages operating in class A amplification with a highdegree of degenerative feed-back in each stage. Input sensitivity iscontrolled by changing the gain of transistor 17 through a change in itsoperating point by means of a manually controlled potentiometer 13.

A preamplifier output at the collector of transistor 19 is reflectedthrough capacitors 21 to the base of a transistor 23. Transistor 23,along with a transistor 25, cooperates to form a voltage amplifierhaving inherent compression properties. Transistor 23 operates tocontrol the current flowing in the emitter of transistor 25 and transitor'25 operates as a grounded base voltage amplifier.

The signal appearing at the base of transistor 23 is AC. and the swingin the range of tenths of a volt. In the no-signal condition, bothtransistors 23 and 25 are biased'at approximately the same voltage, andequal currents will flow in both. When conductivity is decreased orincreased in transistor 23 by virtue of the A.C. signal, the change incurrent flow through transistor 23 will eifect the transistor 25 in theinverse manner since these transistors form a parallel circuit.

The voltage at the collector of 25 will vary in the same manner as theinput signal at the base of transistor 23. A resistor 33 having a valueof 2,000 ohms has connected in parallel thereto a capacitor 49 forreflecting these A.C. voltage changes to a circuit 51.

Also connected by capacitors 31 to the collector transister 23 is anetwork of AC. signal sensing transistors 39', 45, and 43. Transistors39 and 43 are connected by diodes 37 and 41 to the capacitors 31, andthese transistors are normally biased near conduction when no A.C.signal is applied across capacitors 31.

When a positive change is sensed at the collector of transistor 25, thediode 37 couples the same to transistor 3? and causes conduction. Whentransistor 3? conducts, the collector drops toward ground potential, andthe transistor 45, normally biased off, conducts and raises thepotential at its collector.

In a similar manner, negative changes at the collector of transistor 2-5cause conduction in transistor 43 which also generates a positivevoltage signal at its output.

' These positive pulses from transistors 43 and 45 indicative ofpositive and negative swings of voltage at the collector of transistor25 are coupled to an integrator circuit 61, '59, 63, and 65. As thesepositive pulses cause conduction in transistor 61 and establish a givenvoltage at the collector thereof, the capacitor 63 will, by contributingand accepting current at the base, tend to keep the transistor 61 at asteady conducting stage so that peaks of voltage from transistors 43 andwill not affect the operation. This is a Miller type integrator.

An incandescent lamp 59 connected to the collector of transistor 61 actsas a resistance integrator in that pulses of random nature which maycause conduction in transistor 61 will not cause a voltage drop acrosslamp 59, and thus the voltage at the collector of transistor 61 willstay at ground potential.

When the signal at the collector of transistor 25 increases in amplitudeother than for short peaks, the voltage at the collector of transistoras will drop to some value less than ground potential.

A bilateral transistor 53, i.e., having two emitters, is normallymaintained in a given state of conductivity by the potential applied tothe base thereof by the lamp 59. When there is no integrating action ofintegrator 61 and the base is at ground potential, transistor 53 isnonconducting and thus presents a high impedance to any signal appliedto capacitor 4%. Thus for a no-change signal condition at the base ofcollector 25, the circuit 51 is a high impedance.

For signal conditions which vary positively and cause integration by theintegrator 61;, the transistor 53 is biased more conducting. Theincreased current through transistor 25 sees a lower impedance throughcapacitor 49 which prevents the voltage at collector 25 from rising. Inthis the emitter of transistor 53 which is used is 57,

For negative type signal excursions the same result occurs, but here theemitter is 55, and the circuit 51 transfers current through capacitor 49to raise the voltage output. 7

The output of transistor s1 is the AGC voltage and governs theconduction of a bilateral transistor 53 which reflects an impedance tothe preamplifier output stage 25 which is an inverse function of the AGCvoltage. The preamplifier gain of the transistor 25 is variable as afunction of the load. Therefore, by changing the effective impedance ofthe amplifier 25, the output gain of the transistor 25' may be varied,and the input speech frequency may be compressed into the uniformenvelope.

Increased compression voltage results in increased conduction and lowerimpedance which lowers the gain of the last stage 25 so controlling theoutput amplitude without excessive distortion. The result is to speed upthe compression action without introducing oscillations or distortion.Thus a relatively constantamplitude signal appears at the base of a PNPtransistor 25 which drives an output stage 27.

As the pressure time pattern of the sawtooth waveform varies from amaximum to a minimum, the amplitude of the output speech envelope willalsovary in amplitude from a maximum to a minimum. While this pattern ofrising and falling is not readily apparent when varying the waveform atthe collector of transistor 25, the amplitude detecting transistors 43and 45 will provide an output pulse at low and high levels. These pulsesare used as previously explainedto bias the transistor 53 to the properconductive state to generate a uniform output envelope at the output atthe collector of transistor 25. Thus while it may appear paradoxical atfirst, it is also apparent that the bias on transistor 53 must be keptat the proper level by variations in the input which the circuit 53 isto control. These are of course small variations which are detected bytransistors 43 and 39 and are merely sufificient to keep transistor 53properly biased.

Thus while transistor 3 is responsive to the positive peaks of amplitudeof the generated speech, the output has been taken from the negativeamplitude detecting circuit 4-3. This is a practical arrangement sincethe microphone produces a more negative voltage for increased soundpressure, and the preamplifier has an even number of stages andtherefore causes no inversion.

The output of transistor 25, FIG. la, is supplied to a transistor 27which supplies an output 29 at its emitter. The envelope of speechfrequencies is supplied to an armplifier 67, FIG. lb, which isresponsive only to the low frequencies of the voice and then to anintegrating shaper 69 which generates a raised output in response tothese low frequencies. The output from shaper 69 is used as will bedescribed subsequently as an interlock to prevent an output in theabsence of voice. The details of this circuit will be found inapplication Serial No. 161,089 to Genung L. Clapper.

The pulses at the fundamental frequency at output 47 are coupled througha diode 71, FIG. 1b, to an integrating network consisting of resistor 73and capacitor 81. The positive-going pulses on line 47 charge thecapacitor 81 and start conduction in transistor 77. The transistor 77,when starting into conduction, supplies current to one side of thecapacitor 81. This acts as a smoothing type of integrating device forthe incoming square waves which may be quite ragged because of the highfrequency content of the input signal. Small negative excursions, etc.,on the positive-going waveforms on line 47 will be resisted by thecapacitor 81 which is being held up by the current action of thetransistor 77 on the opposite plate of the capacitor.

The resulting square wave suitably smoothed appears at the collector ofthe transistor 77 and is applied to the base of a transistor 33. Whenthe potential at the collector of transistor 7'7 reaches a valuesufficiently negative, the transistor 83 will be biased into conductionto supply a positive-going pulse through diode to the output line 87,line B, FIG. 2. This positive-going pulse is reflected back throughcapacitor 84 to reinforce the conduction of transistor '77. so that nowboth transistors 77 and 83 are conducting.

The potentiometer 79 can vary the time in which it takes the positivecharge produced on the capacitor 81 to decay. This allows adiflerentiation to be made for masculine and feminine speakers since itis possible that the feminine speaker might produce positive-goingpulses on line 47 with a frequency too high to allow capacitor 81 todischarge. When the capacitor 81 has discharged sufficiently from thepulse on line 47, the potential at the collector of transistor 77 willdrop and bias oil the transistor 83. The diode 85, through which thepulse is transferred into the line 87, was utilized to bias thetransistor 89 to an Off condition. Ordinarily when the transistor 83 isoff, the transistor 39 is biased to conduction by the 12 volts to thebase. Therefore, when the transistor 83 is cut oil and the line 87 dropsto the 12 volts,

a sharp negative excursion is reflected back through the capacitor 84 toinsure cutoff of transistor 77. The circuit 36 therefore has reached astable condition and is ready for the next positive-going pulse on line47.

The output 87, line B, FIG. 2, is applied to a balanced integrator 94from which is derived a voltage proportional to the frequency of thedigital pulse input. This integrator is a novel circuit and differs fromknown former integrators in that the voltage output for no input is thesame as that for a median frequency input. Thus a change from no signalto the median frequency produces no change in the output. This allows aninput to be intermittent with a minimum of delay incurred at thebeginning of each group of pulses. V

The great advantage in using this type of integrator is that no recoverytime is lost in going from a no-signal condition to a normal condition.lnaddition the characteristics of the circuit insure fast response andshort as possible recovery time from abnormal conditions. Any changes infrequencies is promptly reflected in'the change of output voltage.

If there are no pulses present on line 87, capacitors 9i and 93 isolatethe output 87 from DC. voltages so that the points 95 and 99 will not beaffected by DC. conditions. Point 99 will be very near ground potentialor zero volts by virtue of the diode Hi3 and point 95 very near thenegative potential l2 volts by reason of the clamp diode 117. With point99 at zero volts and point 95 at -12 volts, no cutoff bias can besupplied to either transistor since the lNP transistor ill? needs avoltage more positive than zero, and the NPN transistor T needs avoltage more negative than -l2 volts. Both transistors therefore willconduct and base current flows as follows: From ground 1% to the emitterof transistor ill? to the emitter base junction to the base of 107through the resistors ill and 113 to the base of transistor 115 throughthe emitter base diode of the transistor 115 to 12 volts. Transistorcurrent will therefore fiow from ground 1&5, transistor 10?, resistor125, resistor 121, transistor 135 to 12 volts. outputvoltage at output127 to 6 volts since both transistors will be saturated, and there willbe little voltage drop across either one.

The transistor 115 and capacitor 119 combination, as well as thetransistor 107 and capacitor 1% combination, are Miller integrators. AMiller integrator is essentially an integrator having an amplifierconnected to the output, and a degenerative feedback from the output ofthe amplifier to the output of the integrator to insure stability ofoperation.

In the pulse input to the integrators lill and 1439, the negative levelof the input pulses, FIG. 2, will cause conduction in transistor 107 ofa predetermined amount which will be resisted by the positive-goingoutput pulses at the collector of transistor 167 reflected across thecapacitor. By the same token, the positive rise at the base of 107 willbe retarded by the collector current in the opposite phase. Thus thevoltage at the collector will tend to remain constant for pulses havingapproximately 50% duration. As the pulses increase in negative dura-Current flowing in this circuit holds the 6 tion, the transistor M7 willapproach more closely to full conduction, and ground potential will bepresent at the collector.

At the same time that this is happening, the integrator 97 andintegrator lli with transistor works inversely, and transistor llzi willgradually cut oil. Potential at output 127 will then approach ground.

For pulses which have a longer positive duration, the inverse of theabove will occur, and line 127 will approach -12 volts.

While the Miller integrator is well known in vacuum tube technology andthe circuitry justdescribed is substantia ly the entire circuit, itshould be appreciated that the use of two transistors in a complementaryconfigura tion introduces an additional factor. This is theamplification factor which is very large in transistors and would inessence operate to move the output very rapidly to one extreme of outputvoltage or the other dependent on the positive or negative duration ofthe input pulses.

In order to prevent this event, the output 127 is fed backdegeneratively by means of resistors 12?), 111, and till to the inputsof the transistor 197 and transistor 115. These input resistors allowthe output to assume an output voltage that continuously providesinformation as to the input pulse rate.

FIG. 2 illustrates the input waveforms and resulting output voltages.

The pulse chart of FIG. 2 shows the balanced inte-. gnator l with anumber of different pulse conditions. For example, the normal inputcondition with input pulses having a period Pl, the pulses, line A, arethose which appear on line 47 indicative of the fundamental frequency ofthe sawtooth waveform used by the speaker. The pulses, line B, are theintegrated pulses which-appear on the output line 87 of the integratingcircuit. Pulses are shown on the lines C and D, which are the voltageswhich appear at the point 99 and point 95, respectively, of the balancedintegrator. These waveforms, lines C and D, have been labeled biasedcondition and conducting condition so that during the period labeledcond. the transistor ill? connected to point 99, which is aiiected bythe pulses shown on line C, will conduct when the pulse waveform is in adown condition with the l voltage. On the up portion of the pulse, lineC, the transistor 107 will be biased oil.

The waveform, line D, which is applied at point 95, causes the oppositeresults. The transistor 115, which is the NPN type, is cut oil whentransistor 1107 is conducting and vice versa.

A change in frequency to a lower frequency of period P2 results in a 40%bias condition for the PNP transistor it and a 60% conduction periodWhile conversely the NPN transistor will now have 60% for bias and 40%for conduction. Under these circumstances, line B, which is the output127 of FIG. 1b, will rise to -4 volts. For a higher frequency of periodP3, the transistor 3W7 will conduct only 29% of the period while thetransistor lllb' will conduct 89% of the time, and the voltage at theline 127 will drop to -10 volts.

FIG. 3, in part, shows similar waveforms to that shown in FIG. 2. Theoutput 4-7 shown in the first column is indicative of the pulse input,line A, of FIG. 2. The output 127 is the output from the balancedintegrator M and shows that for no-voice condition or steady-voicecondition the output is the same. tion, the output 127 drops asindicated in FIG. 2 to voltages approaching l2 volts. A falling voicewherein the pulse period Pi is more extended in time will pro vide anoutput 127 which rises similar to that shown for period P2 in FIG. 2.The remainder of the chart will be explained subsequent to thedescription of the inflection detection circuit logic. i

The output 1270f the balanced integrator is applied to an input clamp131 which is rendered conducting by an input 129 to the base from theshapes 69, PEG. 15,

On a rising-voice condi greases which provides 12 volts to the base andkeeps the line 127 at -6 volts, regardless of the integrator actionduring the no-voice periods. When voice is present, the clamp 131i isofii, and the output on 127 is applied to a low pass filter 133. Underthe steady-voice condition or no-voice condition, the input will be ator near 6 volts. Under these conditions, the transistor tor the low passfilter which consists essentially of the capacitor resistance network133 and transistor 135 will reject jitter noise on the line 127 and passonly the low frequencies and provide an output 137 at approximately 6volts.

With line 137 in a steady state condition, no changes will be reflectedacross capacitor or capacitor 139, FIG. 10. Under these conditions, thetransistor 14-3,

' having a diode lli5 connected from the base to the emitter, will notconduct, and the PNP transistor 14] will conduct and provide a raisedvolt-age output on line 159. The NPN transistor 149 will be biased toconduction by the connection from ground through resistor to the base,and the emitter, biased at 12 volts, will provide a negative signal atthe collector of transistor 149 and cause conduction in transistor 1555and therefore cause the line 157 to be in a raised voltage condition.Therefore under no-voice or steady-voice condition, both lines 159 and157 will be up and conditioning the AND circuits 161 and 167.

A- negative change on line 12-7, PEG. lb, which it will be remembered isa rising inflection, will be coupled to the line 1137, and this negativechange will cut oft the transistor 149 and this in turn cuts offtransistor and causes the line 157 to drop to a low voltage output whichis applied to the AND circuit 167. The negative volt-age swing atemitter of transistor 143 will be clamped by the current flowing in thediode 145 connected to ground.

By the same token, a positive change on the line 137 indicating afalling inflection will be coupled through the capacitors 139 and andcause conduction in the transistor 143, resulting in nonconduction ofthe transistor to cause the line 159 to drop. This signal is applied toAND circuit in.

Summarizing, the lines 159 and 157 are usually up and one or the otherdrops out for a rising inflection or for a falling inflection. Theseoutputs are applied to the AND circuits 1611 and 3167 in conjunctionwith an input 129 from the voice circuit and AND circuits 161 and 167will not be enabled until there is voice. When both inputs to the ANDcircuits 1-61 and i are up, the transistor 163 or transistor 169 isconditioned to conduct, and an appropriate output is provided on line1-55 or line 171.

As indicated previously, the output on line 127, FIG. lb, is the samefor a steady voice at median frequency or for no voice input. It will beremembered that the transistor 131 is conditioned by line 1129,indicating the presence of a voice. Therefore, if no voice is present,the lines 159 and 157 are up as indicated for no voice or steady voiceand connected to the AND circuits 163i and 167. It will be rememberedunder the no-voice condition however that the line 129 Will be down, andthe AND gates will not be unabled so that under no-voice condition thelines .165 and 171 will be down. Under the steady-voice condition, theline 129 will be up, and the AND circuits 161 and 1 67 will be enabledand both lines 165 and 171 will be up for an indication of stead voice.For the conditions 'ofrising voice and falling voice, FIG. 3 showsclearly the outputs which will be present on lines 165 and 171 undereach of these conditions.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the -rt that the foregoing and othechanges in form anddetails may be made therein without departing from the spirit and scopeof the invention.

' What is claimed is: 1

ll. An inflection detection system for the fundamental frequencycontained in a complex wave comprising:

(a) amplifier means responsive to said complex Wave for generating an oput signal;

(b) anipiitude detecting means responsive to variations in the output ofsaid amplifier for generating an output signal pulse;

to) an integrating network responsive to pulses from said amplitudedetecting means for applying a corrective signal to said amplifier tovary the amplification of the same to insure a uniform intensity outputsignal;

(d) an integrating pulse shaper connected to said ampiitude detectingmeans and responsive to pulses therefrom to generate an output pulsehaving a predetermined duration;

(e) a balanced integrator connected to said integrating pulse shaper andresponsive to said output pulses for generating an output voltageindicative of the frequency of the output pulses from said amplitudedetecting means; and

(if) an inflection circuit responsive to said output voltage of saidbalanced integrator for generating an indication of variation infrequency from a median frequency.

2. The apparatus of claim 1 wherein said balanced integrator includes:

(a) a first signal responsive device;

(b) means for DC. biasing said device to conduction wherein a lowimpedance path is provided, said bias means being so proportioned as tocause conduction in said first signal responsive device on one excursionof an input pulse and to be cut off on the other excursion;

(c) an input circuit connected to said integrating pulse shaper;

(d) means for isolating said first signal responsive device from DC.signals present at said input circuit;

(e) an integrating circuit connected to said first signal responsivedevice for establishing a voltage proportional to the frequency or" saidpulses from said integrating pulse shaper; I

(t) a second signal responsive device;

(g) means for DC. biasing said device to conduction wherein a lowimpedancepath is provided, said bias means being so proportioned as tocause conduction in said second signal responsive device on oneexcursion of an input pulse and to be cut off on the other excursion;

(h) means for isolating said second signal responsive device from DC.signals present at said input circuit;

(i) an integrating circuit connected to said second signal responsivedevice for establishing a voltage proportional to the frequency of saidpulses from said integrating pulse shaper;

(j) means for connecting said first and second signal responsive devicesin series relation; and

(k) means for establishing an output circuit at the connection to saidtwo devices.

3. The apparatus of claim 2 wherein said inflection circuit includes:

(a) a first voltage responsive device biased to nonconduction andresponsive to positive increments of voltage to become conducting; and

(b) a second voltage responsive device biased to conduction andresponsive to negative increments of voltage to become non-conducting,wherein the change in output signal of each of said devices isindicative of the fundamental frequency change at that time.

4. A balanced integrator operative to provide a DC.

output signal indicative of an input frequency including:

v( a) a first signal responsive device;

(b) means for DC. biasing said device to conduction wherein a lowimpedance path is provided, said bias means being so proportioned as tocause conduction in said first signal responsive device on one excursionof an input pulse and to be cut off on the other excursion;

(c) an input circuit to said balanced integrator;

(d) means for isolating said first signal responsive device from DC.signals present at said input circuit;

(e) an integrating circuit connected to said first signal responsivedevice for establishing a voltage proportional to the frequency ofpulses at said input circuit;

(f) a second signal responsive device;

(g) means for DC. biasing said device to conduction wherein a lowimpedance path is provided, said bias means being so proportioned as tocause conduction in said second signal responsive device on oneexcursion of an input pulse and to be cut off on the other excursion;

(h) means for isolating said second signal responsive device from DC.signals present at said input circuit;

(i) an integrating circuit connected to said second signal responsivedevice for establishing a voltage proportional to the frequency ofpulses at said input circuit;

(j) means for connecting said first and second signal responsive devicesin series relation; and t (k) means for establishing an output circuitat the connection to said .two devices whereby the output signal for noinput signal is the same as a median frequency input signal.

5. The apparatus of claim 4 further including:

(a) a first voltage divider network connected from said output circuitto the input of said first voltage responsive device; and

('b) a second voltage divider network connected from said output circuitto the input circuit of said second voltage responsive device wherebyoperation of said voltage responsive device will be stabilized.

6. An inflection detection system for the detection of changes in thefundamental frequency of the voice in- 4 eluding:

(a) an amplifier for receiving said complex wave and providing an outputsignal of uniform intensity; (b) said amplifier including a feedbackcircuit to inlb sure uniform intensity in the output signal of saidamplifier;

(c) amplitude detecting means in said feedback circuit operative togenerate an output signal in response to variations in intensity of saidcomplex wave wherein the output signal is indicative of the fundamentalfrequency in said complex waveform;

(d) an integrating pulse shaper connected to said amplitude detectingmeans and responsive to pulses therefrom to generate an output pulsehaving a predetermined duration;

(e) a balanced integrator connected to the output of said integratingpulse shaper and responsive to said pulses for generating an outputvoltage indicative of the frequency of output signal from said amplitudedetecting means;

( f) a clamp connected to the output circuit of said balanced integratorand responsive to the absence of the voice band in said speech fornullifying the output voltage of said integrator; and

(g) an inflection circuit responsive to said output voltage of saidbalanced integrator for generating an indication of variation infrequency from a median frequency.

7. The apparatus of claim 6 wherein said inflection circuit includes:

(a) a first voltage responsive device biased to nonconduction andresponsive to positive increments of voltage to become conducting; and r(b) a second voltage responsive devicefbiased to conduction andresponsive to negative increments of voltage to become non-conducting,wherein the change in output signal of each of said devices isindicative of the fundamental frequency change at that time.

References Cited by the Examiner UNITED STATES PATENTS 2,284,102 5/42R-osencrons 33085 2,710,348 6/55 Baum et al. 330109 2,852,624 9/58 Young330-109 ROBERT H, ROSE, Primary Examiner.

1. AN INFLECTION DETECTION SYSTEM FOR THE FUNDAMENTAL FREQUENCYCONTAINED IN A COMPLEX WAVE COMPRISING: (A) AMPLIFIER MEANS RESPONSIVETO SAID COMPLEX WAVE FOR GENERATING AN OUTPUT SIGNAL; (B) AMPLITUDEDETECTING MEANS RESPONSIVE TO VARIATIONS IN THE OUTPUT OF SAID AMPLIFIERFOR GENERATING AN OUTPUT SIGNAL PULSE; (C) AN INTEGRATING NETWORKRESPONSIVE TO PULSES FROM SAID AMPLITUDE DETECTING MEANS FOR APPLYING ACORRECTIVE SIGNAL TO SAID AMPLIFIER TO VARY THE AMPLIFICATION OF THESAME TO INSURE A UNIFORM INTENSITY OUTPUT SIGNAL; (D) AN INTEGRATINGPULSE SHAPER CONNECTED TO SAID AMPLITUDE DETECTING MEANS AND RESPONSIVETO PULSES THEREFROM TO GENERATE AN OUTPUT PULSE HAVING A PREDETERMINEDDURATION; (E) A BALANCED INTEGRATOR CONNECTEDD TO SAID INTEGRATING PULSESHAPER AND RESPONSIVE TO SAID OUTPUT PULSES FOR GENERATING AN OUTPUTVOLTAGE INDICATIVE OF THE FREQUENCY OF THE OUTPUT PULSES FROM SAIDAMPLITUDE DETECTING MEANS; AND (F) AN INFLECTION CIRCUIT RESPONSIVE TOSAID OUTPUT VOLTAGE OF SAID BALANCED INTEGRATOR FOR GENERATING ANINDICATION OF VARIATION IN FREQUENCY FROM A MEDIAN FREQUENCY.